Chapter III: Part 3

At a transit, astronomers confine their attention to one particular phase—the moment, namely, when Venus just seems to lie wholly within the outline of the sun’s disc. This at least was what Halley and Delisle both suggested as desirable. Unfortunately, Venus had not been consulted, and when the time of the transit came she declined to enter upon or leave the sun’s face in the manner suggested by the astronomers. Consider, for example, her conduct when entering on the sun’s face:—

At first, as the black disc of the planet gradually notched the edge of the sun’s disc, all seemed going on well. But when somewhat more than half of the planet was on the sun’s face, it began to be noticed that Venus was losing her rotundity of figure. She became gradually more and more pear-shaped, until at last she looked very much like a peg-top touching with its point the edge of the sun’s disc. Then suddenly—‘as by a lightning flash,’ said one observer—the top lost its peg, and then gradually Venus recovered her figure, and the transit proceeded without further change on her part until the time came for her to leave the sun’s face, when similar peculiarities took place in a reversed order.

Here was a serious difficulty indeed. For when was the moment of true contact? Was it when the peg-top figure seemed just to touch the edge of the sun? This seemed unlikely, because a moment after the planet was seen well removed from the sun’s edge. Was it when the rotund part of the planet belonged to a figure which would have touched the sun’s edge if the rotundity had been perfect elsewhere? This, again, seemed unlikely, because at this moment the black band connecting Venus and the sun was quite wide. And, besides, if this were the true moment of contact, what eye could be trusted to determine the occurrence of a relation so peculiar? Yet the interval between this phase and the final or peg-top phase lasted several seconds—as many as twenty-two in one instance in 1769—and the whole success of the observation depended on exactness within three or four seconds at the outside.

We know that Venus will act in precisely the same manner in 1874. If we had been induced to hope that improvements in our telescopes would diminish the peculiarity, the observations of the transit of Mercury, in November 1868, would have sufficed to destroy that hope, for even with the all but perfect instruments of the Greenwich Observatory, Mercury assumed the peg-top disguise in the most unpleasing manner.

It may be asked, then, What do astronomers propose to do in 1874 to prevent Venus from misleading them again as she did in 1769? Much has already been done towards this end. Mr. Stone undertook a series of careful researches to determine the law according to which Venus may be expected to behave, or to misbehave herself; and the result is, that he has been able to tell the observers exactly what they will have to look for, and exactly what it is most important that they should record. In 1769, observers recorded their observations in such doubtful terms, owing to their ignorance of the real significance of the peculiarities they witnessed, that the mathematicians who had to make use of those observations were misled. _Hinc illæ lacrymæ._ Hence it is that an undeserved reproach has fallen upon the ‘exact science.’

The amount of the error resulting from the misinterpretation of the observations made in 1769 was, however, very small indeed, when its true character is considered. It is, indeed, easy to make the error seem enormous. The sun’s distance came out some four millions of miles too large, and that seems no trifling error. Then, again, the resulting estimate of the distance of Neptune came out more than a hundred million miles too great; while even this enormous error was as nothing when compared with that which resulted when the distances of the fixed stars were considered.

But this is an altogether erroneous mode of estimating the effect of the error. It would be as absurd to count up the number of hairs’ breadth by which the geographer’s estimates of the length and breadth of England may be in error. In all such matters it is relative and not absolute error we have to consider. A microscopist would have made a bad mistake who should over-estimate the length of a fly’s proboscis by a single hair’s breadth; but the astronomer had made a wonderfully successful measurement of the sun’s distance who deduced it within three or four millions of miles of the true value. For it is readily calculable that the error in the estimated relative bearing of the sun as seen from opposite sides of the earth corresponds to the angle which a hair’s breadth subtends when seen from a distance of 125 feet.

The error was first detected when other modes of determining the sun’s distance were applied by the skilful astronomers and physicists of our own day. We have no space to describe as fully as they deserve the ingenious processes by which the great problem has been attacked without aid from Venus. Indeed, we can but barely mention the principles on which those methods depend. But to the reader who takes interest in astronomy, we can recommend no subject as better worth studying than the masterly researches of Foucault, Leverrier, and Hansen upon the problem of the sun’s distance.

The problem has been attacked in four several ways. First, the tremendous velocity of light has been measured by an ingenious arrangement of revolving mirrors; the result combined with the known time occupied by light in travelling across the earth’s orbit immediately gives the sun’s distance. Secondly, a certain irregularity in the moon’s motion, due to the fact that she is most disturbed by the sun when traversing that half of her path which is nearest to him, was pressed into the service with similar results. Thirdly, an irregularity in the earth’s motion, due to the fact that she circles around the common centre of gravity of her own mass and the moon’s, was made a means of attacking the problem. Lastly, Mars, a planet which, as we have already mentioned, approaches us almost as nearly as Venus, was found an efficient ally.

The result of calculations founded on these methods showed that the sun’s distance, instead of being about 95,000,000 miles, is little more than 91,500,000 miles. And recently a re-examination of the observations made upon Venus in 1769 led Mr. Stone to believe that they point to a similar result.

Doubtless, however, we must wait for the transit of Venus in 1874 before forming a final decision as to the estimate of the sun’s distance which is to take its place in popular works on astronomy during the next century or so. Nothing but an unlooked-for combination of unfavourable circumstances can cause the failure of our hopes. Certainly, if we should fail in obtaining satisfactory results in 1874, the world will not say that the generosity of the English Government has been in fault, since it would be difficult to find a parallel in the history of modern science to the munificence of the grant which has been made this year for expeditions to observe a phenomenon whose interest and importance are purely scientific.

(From _St. Paul’s_, October 1869.)

FOOTNOTES:

[3] The reader will remember the time at which the essay appeared. For several reasons it seems well to leave the essay unaltered. In the second series of Light Science a later stage is presented, and the account is carried up to the present date in my work on _The Transits of Venus_.

[4] It is held to be of the utmost importance that all the observing parties should use similar telescopes.

_BRITAIN’S COAL CELLARS._

It would have been deemed a strange thought in the days of the Tudors to suggest that England’s greatness would one day depend,—or seem to depend,—on her stores of coal, a mineral then regarded as only an unpleasant rival of the wood-log for household fires. When Shakespeare put into the mouth of Faulconbridge the words—

This England never did, nor never shall,
Lie at the proud foot of a conqueror,
But when it first did help to wound itself,

he would have thought it a singular proviso that England should be watchful of her coal stores if she would preserve her position among the nations. And yet there is a closer connection between the present greatness of Britain and the mighty coal cellars underlying certain British counties than we are commonly prepared to acknowledge. Saxon steadiness and Norman energy have doubtless played their part in placing Britain in the position she now holds; but whatever may have been the case in past ages of our history, it is certain that at present there is much truth in Liebig’s assertion that England’s power is in her coal. The time may come again, as the time has been, when we shall be less dependent on our coal stores,—when bituminous bankruptcy will not be equivalent to national bankruptcy; but if all our coal mines were at this moment rendered unworkable, the power of England would receive a shock from which it would be ages in recovering.

I have quoted an assertion made many years since by Baron Liebig. The assertion was accompanied by another not less striking. ‘Civilisation,’ he said, ‘is the economy of power; and English power is coal.’ It is on this text that I propose now to comment. There has recently been issued a Blue Book, bearing in the most important manner on the subject of England’s coal-supply. For five years fifteen eminent Commissioners have been engaged in examining the available evidence respecting the stores of coal contained in the various coal-fields of Great Britain. Their inquiries were commenced soon after the time when the fears of the country on this subject were first seriously awakened; and were directed specially to ascertain how far those fears were justified by the real circumstances of the case. It will be well to compare the various opinions which were expressed before the inquiries were commenced, with the results which have now been obtained.

In the first place it should be noticed that the subject had attracted the attention of men of science many years ago. Some forty years[5] have passed since Dr. Buckland, in one of the Bridgewater Treatises, pointed to the necessity for a careful examination of our coal stores, lest England should drift unawares into what he called ‘bituminous bankruptcy.’ At that time the quantity of coal raised annually in England amounted to but about forty millions of tons. Ten years later the annual yield had risen to about fifty millions of tons; and then another warning voice was raised by Dr. Arnold. Ten more years passed, and the annual yield had increased to 83,635,214 tons, when Mr. Hull made the startling announcement that our coal stores would last us but about two centuries, unless some means were adopted to check the lavish expenditure of our black diamonds.

But it was undoubtedly the address of Sir W. Armstrong to the British Association, in 1863, which first roused the attention of the country to the importance of the subject. ‘The greatness of England,’ he said, ‘depends much upon the superiority of her coal, in cheapness and quality, over that of other nations. But we have already drawn from our choicest mines a far larger quantity of coal than has been raised in all other parts of the world put together; and the time is not remote when we shall have to encounter the disadvantages of increased cost of working and diminished value of produce.’ Then he summed up the state of the case as he viewed it. ‘The entire quantity of available coal existing in these islands has been calculated to amount to 80,000 millions of tons, which, at the present rate of consumption, would be exhausted in 930 years; but with a continued yearly increase of 2¾ millions of tons would only last 212 years.’

Other statements were not wanting, however, which presented matters in a more favourable light. Mr. Hussey Vivian, M.P., expressed the opinion that South Wales alone could supply all England with coals for 500 years. Mr. R. C. Taylor, of the Geological Society, said that our coal stores would suffice for 1,700 years. And there were some who adopted a yet more sanguine view of our position.

On the other hand, Mr. Edward Hull, of the Geological Survey, calculated that with an increase of but one million and a half of tons per annum—considerably less than even the average increase for the preceding decade[6]—our coals would last us but a little more than 300 years. Mr. Stanley Jevons, in his masterly treatise on ‘The Coal Question,’ adopted a mode of considering the increase, which has led to an even more unpleasant conclusion than any hitherto obtained. He observed that the quantity of coal raised in successive years is not merely increasing, but the amount of increase is itself increasing. ‘We, of course, regard not,’ he said, ‘the average annual arithmetical increase of coal consumption between 1854 and 1863, which is 2,403,424 tons, but the average rate per cent. of increase, which is found by computation to be 3·26 per cent.’ That is to say, for every hundred tons of coal consumed in one year, 103¼ tons, or thereabouts, would be consumed in the next—taking one year with another. Without entering into technicalities, or niceties of calculation, it is easy to show the difference between this view of the matter and a view founded only on the average increase during so many years. Consider 10,000 tons of coal sold in one year, then Mr. Stanley Jevons points out that instead of that amount, 10,326 would be sold in the next; and so far we may suppose that the other view would agree with his. But in the next, or third year (always remembering, however, that we must take one year with another), the increase of 326 tons would not be merely doubled, according to Mr. Stanley Jevons; that is, the consumption would not be only 10,652 tons:—the 10,000 of the second year would be replaced by 10,326 tons in the third year, and the remaining 326 would be increased by 3¼ tons for each hundred, or by rather more than 10½ tons; so that in all there would be 10,662¼ tons, instead of 10,652. Now the difference in this third year seems small, though when it is applied to about nine thousand times 10,000 tons it is by no means small, amounting in fact to 95,000 tons; but when the principle is extended to sequent years its effects assume paramount importance. The small increase is as the small increase of a farthing for the second horseshoe-nail in the well-known problem. The effects, after a few years have passed, correspond to the thousands of pounds by which the last shoe-nails of that problem increase the cost of the horse. As Mr. Leonard Lemoran points out in the paper mentioned in the above note, if the assumed rate per cent. of increase continue, ‘we should draw in the year 1900 from our rocks more than 300 millions of tons, and in 1950 more than 2,000 millions.[7] About 300,000 miners are now (1866) employed in raising rather more than 92 millions of tons of coals; therefore more than eight million miners would be necessary to raise the quantity estimated as the produce of 1950. One-third of the present population of Great Britain would be coal miners.’ Or as Mr. Jevons himself sums up our future, ‘If our consumption of coal continue to multiply for 110 years at the same rate as hitherto, the total amount of coal consumed in the interval would be 100,000 millions of tons.’ Now as Mr. Hull estimated the available coal in Great Britain, within a depth of 4,000 feet, at 83,000 millions of tons, it followed that, adopting Mr. Jevons’s mode of calculation, a century would exhaust ‘all the coal in our present workings, as well as all the coal seams which may be found at a depth of 1,500 feet below the deepest working in the kingdom.’ It should be added, however, that Mr. Stanley Jevons mentioned 200,000 millions of tons as the probable limit of the coal supplies of Great Britain.

The opinion of Mr. Jevons respecting the probable rate of increase of our consumption was not accepted by the generality of those who examined the subject in 1865 and 1866. There were some, indeed, who considered that the assumption was ‘absurd in every point of view.’ In one sense, indeed, Mr. Jevons himself would have been ready to admit that his estimates would not be justified by the result. The observed rate of increase could not possibly be maintained beyond a certain epoch, simply because there would not be enough men to work the coal mines to the extent required. But, regarding the increase as indicating the requirements of the kingdom, it would matter little whether the necessary supply failed for want of coal or for want of the means of raising the coal. In other words, removing the question from the arena of geological dispute, and considering only the requirements of the country, we should have this disagreeable conclusion forced upon us, if Mr. Jevons’s estimate is just, that England will not be able, a century, or even half a century hence, to get as many coals from her subterranean cellars as she will then require. She may have the coals, but she will not have men enough to bring them to bank.

It is, perhaps, in this aspect, that the question assumes its chief interest for us. Rightly understood, the statements of Mr. Jevons were of vital importance; so important, indeed, that the nation might have looked forward to the results of the Commission much as a patient would await the physician’s report of the result of a stethoscopic examination. The power of the nation residing—for the nonce at least—in her coal, the enforced consumption of coal at a rate which cannot be maintained (from whatever cause), means to all intents and purposes the decline and approaching demise of England’s power as a nation. Furthermore, apart from all inquiries such as the Commissioners undertook to make, the mere statement of the successive annual yields was to be looked upon as of vital interest, precisely as the progressive waste of a consumptive patient’s strength and substance suggests even more serious apprehensions than the opinion of the physician.

I have said that many eminent authorities held that the rate of increase assumed by Mr. Jevons would not actually prevail. But some went farther, and questioned whether the average annual arithmetical increase of the lately passed years would continue even for the next few years after the publication of Mr. Jevons’s work. ‘Such a continued increase as that, which has taken place during the last five years,’ wrote an excellent practical authority, ‘cannot continue for the next ten years,’—far less, therefore, that increasing rate of increase which Mr. Jevons had assumed. The same writer went farther even than this. For, after pointing out that the exportation of coal would probably be soon reduced, rather than undergo, as during the past, a steady increase, he added that ‘on every side there were evidences of the most decided character, warranting the supposition that the annual exhaustion of our coal fields would not at any period much exceed the hundred million tons which it had nearly reached’ (in 1866).

One of the most interesting questions, then, which the Commissioners were called upon to decide was, whether, at least during the period of their labours, the anticipations of Mr. Jevons would be fulfilled or not. It is easy to compare his anticipations with those above quoted; or rather, it is easy to determine whether Mr. Jevons’s theory of an increasing increase, or the theory of a uniform average increase, accords best with the experience of the last five years. To make the comparison fairly we must adopt the figures on which his own estimate was founded. We have seen that he rejected the annual increase of 2,403,424 deduced from the records of the nine preceding years, and adopted instead an increase of 3¼ per cent. year by year, taking one year with another. His own calculations gave for this year 1871 a consumption of 118 millions of tons,—an enormous increase on the annual consumption when he wrote. According to the view he rejected, the consumption for the year 1871 is easily computed, though slightly different results will be obtained, according to the year we choose to count from. The annual increase above mentioned gives an increase of 24,034,240 tons in ten years, and if we add this amount to the consumption in 1861 (83,635,214 tons) we obtain for the year 1871 a consumption of 107,669,454 tons. On the other hand, if we add eight years’ increase to the consumption of 1863 (88,292,515 tons), we obtain 107,519,907 tons.[8] It will be seen that there is an important difference between the consumption for 1871, as estimated according to Mr. Jevons’s view, and according to the average rate of increase in the nine preceding years. As the matter stood in 1865, the great question concerning the consumption of the year 1871 would have been,—whether it would be nearer 118 millions, the estimate of Mr. Jevons; or to 107½ millions, the estimate, according to the annual rate of increase; or, lastly, to a number of tons, not much, if at all, exceeding 100 millions?

The answer of the Commissioners comes in no doubtful terms. Judging from the consumption during the four years ending in 1870, the estimated consumption for the year 1872 is no less than 115 millions, an amount approaching Mr. Jevons’s estimate much more nearly than could be desired. Indeed, if we consider the imperfect nature of the statistics on which he founded his calculations, the agreement between his estimate and the observed result must be regarded as surprisingly close. Remembering the conclusion to which Mr. Jevons came with respect to the period for which our coal stores would last, and noticing the close agreement thus far between his anticipations and the result, we can well understand the warning tone of the report issued by the Commissioners. ‘Every hypothesis,’ they say, ‘must be speculative, but it is certain that if the present rate of increase in the consumption of coal be indefinitely continued, even in an approximate degree, the progress towards the exhaustion of our coal will be very rapid.’ Let it be remembered that the Commission was issued at the instance of those who took the more sanguine view, and that it included within its ranks such eminent authorities as Sir William Armstrong, Sir Robert Murchison, Professor Ramsay, Mr. John Hunt, and others of like experience in the subject under inquiry.

If, in the next place, we compare Mr. Jevons’s estimate of the quantity of coal available for use with the result obtained by the Commissioners, we find little to restore our confidence in the extent of time during which our coal stores may be expected to last. We have seen that 200,000 millions of tons had been supposed to be available; but the Commissioners find that ‘we now have an aggregate of 146,480 millions of tons, which may be reasonably expected to be available for use.’ Again, it had been supposed that our coal mines could be worked to a depth of 4,000 feet, or to an even greater depth. ‘The difficulties in the way of deep mining,’ wrote Mr. Lemoran in 1866, ‘are mere questions of cost. It is important to notice that the assumption of 4,000 feet as the greatest depth to which coal can be worked, on account of the increase of temperature, is purely voluntary. The increase has been calculated at a rate for which there is no authority; and while we are saying our coal-beds cannot be worked below 4,000 feet, a colliery in Belgium has nearly approached that depth, and no inconvenience is experienced by the miners.’ But the Commissioners state that at a depth of only 2,419 feet in the Rosebridge mine (the deepest in England), the temperature is 94 degrees of Fahrenheit, or within four degrees of blood heat. ‘The depth at which the temperature of the earth would amount to blood heat,’ they add, ‘is about 3,000 feet.’ They express a belief that by the ‘long wall system’ of working (a system as yet seldom adopted in the chief northern mines) it will be possible to reach a depth of 3,420 feet before this heat is attained; but it is by no means certain that this will prove to be the case.

On the other hand, it will be well to regard the more promising aspect of the question.

We must not forget, in the first place, that in all matters of statistical research there is room for misapprehension unless careful attention be paid, not merely to the observed facts, but to the circumstances with which those facts are more or less intimately associated. If we consider, for example, the progress of the consumption of our coal during the past fifteen years, we find that a law of increase exists, which is, as we have seen, easily expressed, and which, after being tested by a process resembling prediction, has been singularly confirmed by the result. But if we inquire into the various causes of the great increase in the consumption of coals, we find that while those causes have been increasing in activity—so to speak—to a degree quite sufficient to explain the observed consumption, they are yet such as in their very nature must needs be unable to pass beyond a certain range of increase. Thus the population of Great Britain has been steadily increasing, and at present the annual increase is itself increasing. Then the amount of coal used in inland communication is increasing, not only on account of the gradual extension of the railway network, but also on account of the increase of population, of commerce, and so on. Again, our commerce with other countries has increased with great rapidity since the year 1860, when the French treaty came into operation, and it will continue to increase with the increase of our population, of our means of communication within our own country as well as with foreign countries, and so on. But all these causes of increase are now growing in activity at a rate which must inevitably diminish. Our population cannot increase beyond a certain extent, because the extent of the country will suffice for but a certain number of inhabitants. If emigration do not prevent increase beyond that number, other causes will, or else a much more serious evil than the exhaustion of all our coal stores awaits the country. Again, the requirements of inland communication will before long be so far met that no such rapid extension as is now in progress will be called for. After convenient communication has been established between all parts of the country—whether the process require the formation of new lines or of new services—no important increase can be required. As regards our commerce, its increase depends necessarily on the increase at present going on in the requirements of the country. Year by year Britain has a larger population, and the average requirements of each member of the population are also increasing. But we have seen that the increase of her population is necessarily limited; and although the increase of the requirements of her people may not be (strictly speaking) limited, yet it is manifest that, inasmuch as that increase depends on causes which are themselves approaching a limit, its rate must, after a time, continually diminish. Let it be understood that, when I speak of the requirements of the population, I do not mean only what they must obtain from other countries. The commerce of a country is the expression of the activity with which the nation is ‘earning its living,’ so to speak, and in a given population there is a limit to what is necessary for this purpose, precisely as there is a limit to the sum which an individual person in any given state of life requires for the maintenance of a given family. Indeed, although such comparisons are not always safe, we may in this case compare what may be called the commercial requirements of the nation with the requirements of the head of the family,—a merchant suppose. There are no limits to the degree of wealth which a merchant may _desire_ to gain, but unquestionably there are limits to the income necessary to maintain his house and family and mercantile position. Supposing he were extending his gains far beyond his actual requirements, it would by no means imply his approaching ruin that there was a demonstrable limit to this extension. And in like manner, it would seem that, apart from the limits set by nature to the extension of our population, it need by no means be assumed that if our commerce showed signs of approaching a limit, the downfall of England’s power would be at hand.

In fact, we cannot accept Mr. Jevons’s figures for distant epochs without first inquiring whether it is likely that at those epochs the circumstances on which the consumption of our coal depends will be correspondingly changed. Supposing that 120 millions of tons of coals suffice for the requirements of our present population, we can scarcely believe that 1,440 millions will be needed in 1950, unless we suppose that the population of Britain will be twelve times greater than at present; or that the population will be even greater than this, since the consumption of coal upon our railways could scarcely be expected to increase in proportion to the population. Now no one believes that Britain will number 300 millions of inhabitants in 1950, or in 2950; the country could not maintain half that number, even though all her available stores of coal and iron, and other sources of commercial wealth were increased a hundredfold.

It is a mistake, indeed, to extend the results of statistical research very far beyond the time to which the facts and figures belong. It would be easy to multiply instances of the incorrectness of such a process. To take a single case.—When cholera has been extending its ravages in this country, the statistics of mortality from that cause, if studied with reference to four or five successive weeks, have indicated a law of increase, which is very readily expressed so as to accord with the mortality during those weeks, and perhaps two or three following weeks. But if such a law were extended indefinitely it might be found to imply nothing short of the complete desolation of the country by cholera, within the space of a few months. Thus, if the deaths (from cholera) in five successive weeks were 20, 27, 35, 47, and 63,—numbers corresponding with the general characteristics of cholera mortality in the earlier stages of a visitation,—the weekly mortality a year later, estimated according to the observed percentage of increase, would be more than 173 millions! Now this method of estimation, though leading to this preposterous conclusion as respects a more distant epoch, would probably lead to tolerably correct results for the next week or two after that in which 63 persons died,—the estimated numbers being 84 and 110 for the next two weeks respectively.

It seems to me, therefore, that we are not justified, by the observed seeming fulfilment of Mr. Jevons’s anticipations, in concluding that a hundred years hence the consumption of coals will be 2,000 millions of tons, or that the total consumption during the next 110 years will be 100,000 millions of tons. We might almost as safely infer that because a growing lad requires such and such an increase of food year by year, the grown man will need a similar rate of increase, and the septuagenarian require so many tons and hogsheads of solid and liquid food _per diem_.

At present it does not seem possible to arrive at any definite conclusions respecting the probable consumption of coal in years to come. The range of observation is not sufficiently extended. It seems clear, indeed, that the epoch is not near at hand when the present law of increase will be modified. This is shown by the agreement of the observed results during the past five years with the anticipations of Mr. Jevons. It would be altogether unsafe to predict that the yearly consumption will not rise to 150 or 200 or even 250 millions of tons per annum, or to point to any definite stage at which the present increasing rate of increase will be changed first into uniform (or arithmetical) increase, and thence into a decreasing rate of increase. But it appears to me that no question can exist that these changes _will_ take place. We might even go farther, and regard it as all but certain that the time will come when there will be no annual increase. Nay, unless the history of this country is to differ from the history of all other nations which have attained to great power, the time might be expected to arrive when there will be, year by year, a slow diminution in the commercial activity of Britain, and a corresponding diminution in the exhaustion of her coal stores. There is room for an amazing increase in Britain’s power and greatness, room also for an unprecedented continuance of these attributes, while yet the coal stores of the country remain well supplied.

Let us conceive, for instance, that the greatest annual consumption of coal during the future years of England’s existence as a great nation, should be set at three times her present annual consumption, or at 350 millions of tons. Few will regard this as an unduly low estimate when they remember that it is exceedingly unlikely that the present population of Britain will ever be tripled, and that a triple population could be commercially far more active (in relation to its numbers) than the present population, with no greater consumption of coal per head. Now, to begin with, if this enormous annual consumption began immediately, we should yet (with Mr. Jevons’s assumption as to the quantity of available coal) have 570 years’ lease of power instead of 110. But, as a matter of fact, so soon as we have recognised the principle that there is a limit to the increase of annual consumption, we are compelled to believe that that limit will be approached by a much gentler gradient, so to speak, than the same consumption as attained on Mr. Jevons’s assumption. According to his view, in fact, an annual consumption of 350 millions of tons per annum will be attained early in the twentieth century; but according to the theory which sets such a consumption as the highest ever to be attained, we should place its attainment several hundreds of years later. This is a vague statement, I admit, but the very fact on which I am mainly insisting is this, that the evidence at present in our hands is insufficient as a basis of exact calculation. Now, if we set 500 years hence as the time when the annual consumption of coal will have reached the above enormous amount, we should set the total consumption during those centuries at about one-half that due to an annual consumption of 350 millions of tons. In that case there would still remain coal enough to supply the country for 320 years at the same tremendous rate. In all, on these suppositions, 820 years would be provided for. These would be years of commercial activity far exceeding that of our own day—in fact, they would be years during which Britain would be accumulating wealth at a rate so enormous that at the end of the era she would be not wholly unprovided with the means of supporting her existence as a nation, apart from all reference to her mineral stores. It is, indeed, utterly inconceivable, I think, that Great Britain and her people will ever be _able_ to progress at the rate implied by these suggestions. To conceive of Great Britain as arriving at ruin within a thousand years by the over-rapid exhaustion of her coal stores, is, in fact, equivalent to supposing that she will attain in the interval to a wholly unprecedented—I had almost said a wholly incredible—degree of wealth and power.

As regards the evidence which has been adduced respecting the extent of the available coal supply, it is to be remarked that, on the whole, the result cannot be regarded as unfavourable. The more sanguine views entertained five or six years ago have not, indeed,, been fully justified. Yet our coal supply has been shown to be enormous, even when considered with reference to the continually increasing exhaustion.

But it must be admitted that the question of the depth to which our coal mines may be conveniently or even possibly worked, has an unpleasantly doubtful aspect. Of the stores which the Commissioners regard as available a vast proportion must be mined out from depths far exceeding any which have been at present reached in England. It is not as yet clear how far the increase of depth will add to the cost and risk of working; nor do I propose to discuss a subject which can only be adequately dealt with by those who possess practical knowledge of the details of colliery-working. I will content myself by quoting some remarks on the subject, in an inaugural address delivered by Mr. George Elliot (one of the Royal Commissioners) before the North of England Institute of Mining Engineers in 1868. ‘The great depth,’ he remarked, ‘at which many of our pits are worked, and the vast extent of their lateral ramifications, make it more than ever necessary that we should secure the best mode of rendering the supply of pure air certain, regular, and safe. It is maintained that ventilating by machinery ensures these desiderata; that the nicety with which mechanical appliances may be regulated, the delicate adjustment of power of which they are capable, and the complete safety with which they may be worked, place them far before the system they are intended to supersede. The extent of our coal supply will be materially increased by the improvement of which this is a type.... It is probable that the ordinary means of ventilation—whether by furnace or fan—may be aided by a change in the force or agency employed for the purposes of haulage and other independent work. As an instance of my meaning, I may mention that the apparatus which I have introduced in South Wales, and which, by means of compressed air used as a motive power instead of steam, draws trams and pumps water with complete success, is found to generate ice in an atmosphere which is naturally hot and oppressive. The mechanical usefulness of these new air-engines seems capable of indefinite extension; while, as their cooling properties form a collateral advantage arising out of their use, it is at least possible that they may prove valuable auxiliaries to the more regular means of ventilation in extending the security and promoting the healthfulness of our mines. _The difficulties of ventilation once surmounted, the extent of coal at our disposal is incalculably increased._‘

In the address just quoted there are some striking suggestions as to the possibility of working those coal fields which extend below the sea on our east and west coasts, especially in the counties of Durham, Northumberland, and Cumberland. Mr. Elliot remarks that ‘for all practical purposes these fields are as entirely within the reach of the mining engineer as the ordinary workings out of which coal is hewed.’ It is known that in many districts the coal strata extend ten or twelve miles beyond the shore; and Mr. Elliot believes that by sinking ventilating shafts in the German Ocean the coal below may be safely worked. The idea seems somewhat daring; yet, after the feats of engineering which have been achieved in our day, there seems no valid reason for doubting that at least when the pressure of a failing coal supply begins to be felt, the means will be found for rendering these immense submarine coal stores available. As to the difficulty of transport, Mr. Elliot remarks that, according to his estimates, ‘transport would neither be more costly nor more laborious than it has been in days gone by to convey coal the same distance after it was brought to the surface inland.’ The enormous importance of the subject is shown by the fact that ‘out of the minerals obtainable in Durham alone, one-third,’ Mr. Elliot tells us, ‘may be held to lie under the sea, and that all coalfields having a similar inclination of strata, and bordering on the ocean, will be similarly enlarged. This at once disposes,’ he adds, ‘of some of the fears expressed as to the duration of our coal supply; and while I am quite aware that these theories may be challenged, they are not put forward without due deliberation, and I am content to stake my professional reputation on their practicability.’

With regard to the future of this country, it appears to me that little anxiety need be entertained. Apart from the considerations I have urged, which seem to indicate that our consumption cannot long increase at the same rate as at present, it seems not unreasonable to anticipate that within the next few decades science will find the means of economising our coals in more ways than one. It does not indeed appear likely that any form of fuel will ever take the place of coal; but a portion of the work now derived from the consumption of coal may be expected to be derived in future years from some of the other substances now coming into use. It may be hoped, also, that science may suggest means for bringing coals to the surface with less waste, and even at less cost, than at present. And in other ways the process of exhaustion may be more or less effectively checked.

But while we may thus look somewhat confidently forward, as I judge, to the future of our country, serious questions are suggested as to the future of the human race. The period during which a nation flourishes, long as it seems by comparison with the life of man, yet sinks into insignificance when compared with the period during which civilised men will bear sway upon the earth. The thousands of years during which the coal stores of the earth may be expected to last will pass away, and then the descendants of those now living on the earth will have to trust to other force-supplies than those which we are now using so lavishly. It may seem fanciful to look so far forward, and yet by comparison with the periods which the astronomer deals with in considering the future of our earth, thousands of years are as nothing. As I have said elsewhere, ‘those thousands of years will pass as surely as the thousands which have already passed, and the wants entailed by wastefulness in our day will then be felt, and none the less that for so many years there had been no failure in the supplies contained within the great subterranean storehouse.’ It behoves us to consider thoughtfully the wants even of those distant eras. If the greatest good for the greatest number is to be regarded as the true rule for the conduct of intelligent beings, then unquestionably mere distance in point of time should not prevent us from anticipating the requirements of those remote descendants of ours. We should regard the consciousness of this duty and its performance as signs by which the superiority of our own over less civilised times is partly manifested. As man is in dignity higher than non-intelligent animals, in that he alone provides of his own forethought for the wants of his children, so our generation would be raised in dignity above preceding generations if it took intelligent charge of the wants of its remote descendants. We ourselves are now employing stores of force laid up for us by the unconscious processes of Nature in long past ages. As Professor Tyndall has finely said, we are utilising the Sun of the Carboniferous Epoch. The light ‘which streamed earthwards from the sun’ was stored up for us by the unconscious activity of ‘organisms which living took into them the solar light, and by the consumption of its energy incessantly generated chemical forces.’ The vegetable world of that old epoch ‘constituted the reservoir in which the fugitive solar rays were fixed, suitably deposited, and rendered ready for useful application.’ What the vegetable world did for us unconsciously during the Carboniferous Epoch, the scientific world of our epoch must do for our remote descendants. While we are consuming the stores of force laid up in past ages for our benefit, we must invent the means for obtaining directly from the solar rays fresh and inexhaustible supplies of motive energy.

(From the _St. Paul’s Magazine_, November 1871.)

_THE SECRET OF THE NORTH POLE._

If an astronomer upon some distant planet has ever thought the tiny orb we inhabit worthy of telescopic study, there can be little doubt that the snowy regions which surround the arctic and antarctic poles must have attracted a large share of his attention. Waxing and waning with the passing seasons, those two white patches afford significant information respecting the circumstances of our planet’s constitution. They mark the direction of the imaginary axial line upon which the planet rotates; so that we can imagine that an astronomer on Mars or Venus would judge from their position how it fares with terrestrial creatures. There may, indeed, be Martial Whewells who laugh to scorn the notion that a globe so inconveniently circumstanced as ours can be inhabited, and are ready to show that, if there were living beings here, they must be quickly destroyed by excessive heat. On the other hand, there are possibly sceptics on Venus also who smile at the vanity of those who can conceive a frozen world, such as this our outer planet, to be inhabited by any sort of living creature. But we doubt not that the more advanced thinkers both in Mars and Venus are ready to admit that, though we must necessarily be far inferior beings to themselves, we yet manage to ‘live and move and have our being’ on this ill-conditioned globe of ours. And these, observing the earth’s polar snow-caps, must be led to several important conclusions respecting physical relations here.

It is, indeed, rather a singular fact to contemplate, that ex-terrestrial observers, such as these, may know much more than we ourselves do respecting those mysterious regions which lie close around the two poles. Their eyes may have rested on spots which, with all our endeavours, we have hitherto failed to reach. Whether, as some have thought, the arctic pole is in summer surrounded by a wide and tide-swayed ocean; whether there lies around the antarctic pole a wide continent bespread with volcanic mountains larger and more energetic than the two burning cones which Ross found on the outskirts of this desolate region; or whether the habitudes prevailing near either pole are wholly different from those suggested by geographers and voyagers—such questions as these might possibly, be resolved at once, could our astronomers take their stand on some neighbouring planet, and direct the searching power of their telescopes upon this terrestrial orb. For this is one of those cases referred to by Humboldt, when he said that there are circumstances under which man is able to learn more respecting objects millions of miles away from him than respecting the very globe which he inhabits.

If we take a terrestrial globe, and examine the actual region near the North Pole which has as yet remained unvisited by man, it will be found to be far smaller than many imagine. In nearly all maps the requirements of charting result in a considerable exaggeration of the polar regions. This is the case in the ordinary ‘maps of the two hemispheres’ which are to be found in all atlases. And it is, of course, the case to a much more remarkable extent in what is termed Mercator’s projection. In a Mercator’s chart we see Greenland, for example, exaggerated into a continent fully as large as South America, or to seven or eight times its real dimensions.

There are three principal directions in which explorers have attempted to approach the North Pole. The first is that by way of the sea which lies between Greenland and Spitzbergen. I include under this head Sir Edward Parry’s attempt to reach the pole by crossing the ice-fields which lie to the north of Spitzbergen. The second is that by way of the straits which lie to the west of Greenland. The third is that pursued by Russian explorers who have attempted to cross the frozen seas which surround the northern shores of Siberia.

In considering the limits of the unknown north-polar regions, we shall also have to take into account the voyages which have been made around the northern shores of the American continent in the search for a ‘north-west passage.’ The explorers who set out upon this search found themselves gradually forced to seek higher and higher latitudes in order to find a way round the complicated barriers presented by the ice-bound straits and islands which lie to the north of the American continent. And it may be noticed in passing, as a remarkable and unforeseen circumstance, that the farther north the voyagers went the less severe was the cold they had to encounter. We shall see that this circumstance has an important bearing on the considerations I shall presently have to deal with.

One other circumstance respecting the search for the north-west passage, though not connected very closely with my subject, is so singular and so little known that I feel tempted to make mention of it at this point. The notion with which the seekers after a north-west passage set out was simply this, that the easiest way of reaching China and the East Indies was to pursue a course resembling as near as possible that on which Columbus had set out—if only it should appear that no impassable barriers rendered such a course impracticable. They quickly found that the American continent presents an unbroken line of land from high northern latitudes far away towards the antarctic seas. But it is a circumstance worth noticing, that if the American continents had no existence, the direct westerly course pursued by Columbus was not only not the nearest way to the East Indian Archipelago, but was one of the longest routes which could possibly have been selected. Surprising as it may seem at first sight, a voyager from Spain for China and the East Indies ought, if he sought the absolutely shortest path, to set out on an almost direct northerly route! He would pass close by Ireland and Iceland, and onwards past the North Pole into the Pacific. This is what is called the great-circle route; and if it were only practicable one, would shorten the journey to China by many hundreds of miles.

Let us return, however, to the consideration of the information which arctic voyagers have brought us concerning the north-polar regions.

The most laborious researches in arctic seas are those which have been carried out by the searchers after a north-west passage. I shall therefore first consider the limits of the unknown region in this direction. Afterwards we can examine the results of those voyages which have been undertaken with the express purpose of reaching the North Pole along the three principal routes already mentioned.

If we examine a map of North America constructed in recent times, we shall find that between Greenland and Canada an immense extent of coast-line has been charted. A vast archipelago covers this part of the northern world. Or, if the strangely-complicated coastlines which have been laid down really belong to but a small number of islands, the figures of those must be of the most fantastic kind. Towards the north-west, however, we find several islands whose outlines have been entirely ascertained. Thus we have in succession North Devon Island, Cornwallis Island, Melville Island, and Port Patrick Island, all lying north of the seventy-fifth parallel of latitude. But we are not to suppose that these islands limit the extent of our seamen’s researches in this direction. Far to the northward of Wellington Channel, Captain de Haven saw, in 1852, the signs of an open sea—in other words, he saw, beyond the ice-fields, what arctic seamen call a ‘water sky.’ In 1855 Captain Penny sailed upon this open sea; but how far it extends towards the North Pole has not yet been ascertained.